SLACK’S CHAT FUNCTION IS A TROJAN HORSE FOR BIGGER IDEAS. IT WANTS TO OVERSEE ALL YOUR OTHER BUSINESS SOFTWARE.

To get you in the door, it has a supercharged group chat function, a modern take on the AOL rooms of yore. It runs on your desktop, the web, your phone, and stays in sync as you switch from one to the other. Instead of one big room, it lets you set up channels for various groups and teams, or even for specific functions (like, say, monitoring the @ replies to your company’s Twitter feed). And naturally, there’s private one-to-one messaging as well.

Yet Slack’s well-designed chat function is a trojan horse for bigger ideas. Its ambition is to become the hub at the center of all your other business software. It ties in to many of the applications you use at work: Dropbox, Google Apps, GitHub, Heroku, and Zendesk to name a few. Once they’re all connected, it can keep track of most everything you do with them. Most importantly, it’s got killer search built right in. “Right now, your data ends up a little bit in Twitter, a little bit in Zendesk, a little bit in GitHub,” Stewart says. “Slack is the one mutual platform where all those things come together. That’s the longer-term thinking.”

The payoff is that it makes collaborating way easier than whatever you’re doing now. Let’s say you drop a link to a PDF stored in your folder in your company’s Dropbox. People on your team will see this file pop up in Slack, with a summary, and can click on it to read—right there in the app. Your colleagues can review it, make notes about it, and comment on what you ought to do next without ever leaving the application. One of your team members says, “You really did it, bro! This is a massive thought bomb.” Yay! They adore you.

Not only did Slack make sure the document went to all the right people, but it also indexed the full text of the document, as well as the conversation that took place around it, and attached the conversation to the document in its database. Now: Imagine that weeks pass by. You, sadly, die unexpectedly. Now that you’re gone, your coworkers need to pull up the document, but they have trouble finding it in your disorganized Dropbox folder. So instead they search Slack for “massive thought bomb” and, presto, there it is, along with all your notes and the feedback you received from your team. That’s Slack.

Slack is so beloved that some companies have begun mentioning it as an employment perk alongside on-site massages and bottomless bacon-tray Fridays in their job listings. Like: We have a dry cleaning service, an ice cream parlor, and… Slack.

Since its public debut in February, Slack has been growing at a rate of 5 to 10 percent a week and now has more than 120,000 daily users. Fully 38,000 people from 2000 different organizations pay for the full-featured version of the service. It has so far pocketed $1.5 million in revenue. If just those subscribers keep paying, Slack would pull in $3.5 million a year. But it is adding so many subscribers so fast, that the annual billing projections are growing by $1 million every six weeks. And people do tend to stick around at an astonishing rate: 93 percent of people who try Slack keep using it. So it’s no wonder that the company has raised some $60 million in venture capital—$43 million in April alone.

The thing about working at a hot, well-funded startup these days is that it’s still really hard to staff up. Equity, salary, extravagant benefits packages, and quirky perks (Slack socks!) are simply table stakes.

If you want to attract good people, if you want to impress that highly talented engineer when she walks through the door and strolls into your conference room after visiting the facilities at Dropbox or Airbnb or Uber or any number of other San Francisco-based businesses, your conference room had better be a log cabin.

Anyway, your space had better be nice, otherwise why not just work at Google? Stewart is aware of this, and so he and Cal are spending the day looking at office furniture porn and talking about interior designers.

“Look at this,” Stewart says, pointing to his screen at a long wooden table with recessed bins for power and ethernet, surrounded by a selection of thousand-dollar chairs. “That’s $100,000. Do you think that’s worth $100,000? It looks like shit.”

They are an odd pair, Cal and Stew, when you see them together. Stewart tends toward designer shirts and respectable slacks on top of wing tips, all whites and pastel colors. Cal is a parody of an engineer. He shows up to work in flip-flops and cargo shorts, even on coldish summer days in San Francisco. He’s mostly quiet, but when he speaks it’s in a loud voice, whereas Stewart is very talkative but almost whispers at you. At work, Cal HAMMERS on his keyboard, and HAMMERS and HAMMERS, and occasionally the room lights up in laughter in response to his HAMMERING (or sometimes it’s in response to the miniature drone he flies through the air). Everyone at Slack communicates, naturally, via Slack.

When night comes, Cal and Stewart head to dinner at Bar Agricole, a popular spot for the city’s power-boozing tech elites. The people you’ll bump into there—Ryan Block at a table with Veronica Belmont, Om Malik downstairs in the private room with Nick Bilton and Matt Buchanan and Nicole Perlroth—are the who’s who of right now, unwinding in a casual no-pressure setting. And no wonder. I mean, the food is amazing. Have you even tried the Farinata with purple artichokes, chrysanthemum, and parmesan? Oh, you have to try it. But really it’s about the drinks, the cocktails, man, oh, wow.

The ice!

Hold your glass up to the light, maybe it’s a Whist Cocktail or a House Old Fashioned, and look into it and you won’t see the cube, although it takes up almost the entire glass by volume. It’s a great gaping gaw of unglistening luxury. Artisanal ice. Stewart and Cal are keen to talk ice. Cal has already backed three different bespoke ice makers on Kickstarter and knows his ice.

AND WHY SHOULDN’T THEY HAVE A COLD DRINK? THEY ARE ON TOP OF THE WORLD, HAVING BUILT A TRULY SUBLIME PIECE OF SOFTWARE.

Make ice at high enough pressure and you get something perfectly transparent, just like what you see in this glass. (Or more accurately: just like you don’t see in this glass.) It’s very important that you don’t see it, because the cloudiness in ice—the white of ice—is caused by air. Air pockets increase the surface area of ice, so more of it comes in contact with liquid and thus waters down your very expensive cocktail. Which is bad, according to Cal. Cold is good. Watery is bad. Both are impressed with the ice here at Agricole. It’s very good ice.

And why shouldn’t they have a cold drink? They are on top of the world, having built a truly sublime piece of software. Consider the lowly link. Drop a link to aWashington Post story in an app like HipChat and you’ll see a URL. Drop the link in Slack and what people see is the link, with the name of the publication right under it, followed by the headline, a byline, and a brief summary of the story below that, and a related image. Instead of an unparsable string of characters that may or may not lead to Goatse, you get a working summary of what you’re about to see.

This appears like magic, instantly. But it belies some very sophisticated, very fast things happening behind the scenes. It’s a powerful experience that looks simple, but it speaks to how sleek Slack’s underlying code is. You don’t really see it. It’s very good ice.

“We like making really good software,” Stewart says, explaining why he can be in a software business that specializes in something as boring as business software. “It’s pleasurable,” Cal says, completing the thought.

In October 2012 Stewart walked across Vauxhall Bridge over the Thames in London with an old high school friend, Alexander Gilly. They had been pals since they were teenagers, and a few years earlier, when Stewart was about to embark on Glitch, he called Alexander to come visit in Canada, to brainstorm how the game might work. (What if it all took place in the imagination of 11 giants? Ohhhhhhhh! That’s a great idea!) Now, here in London, he told his longtime friend that he had decided Glitch had to end. “He said he was very sad about it but felt it was the right thing to do,” Alexander says, “because it had become apparent that they weren’t getting the numbers necessary to make it viable.”

It was painful. Later that month, he told his investors and cofounders, and then 48 hours later broke the news to the rest of the team. He gathered his crew in Vancouver and placed a conference call to the handful of employees in San Francisco. He was crying on the phone. They uploaded an archive of all the art, music, player profiles and even the code from the game to a web site—it’s stillthere—and contributed the art and much of the code to the public domain. He helped all his employees find new jobs. And he managed to not burn through the entirety of the money investors had given him.

Now that Glitch has morphed into an actual success, now that Slack is popular with all the cool kids, he’s faced with an opportunity and a challenge to pay back the people who stuck with him—like the employees from Glitch who chose to exercise their options (basically buying into the company when it wasn’t clear it had a future) and now stand to be repaid many times over.

How much they end up with depends on what Stewart decides to do next. “The biggest thing I worry about with Stewart is that he’ll get a compelling offer too early,” says Josh Pritchard, who runs Slack’s analytics. Josh was an early Facebook employee who (let’s be real) is already rich. He thinks Slack is on a similar trajectory, that Stewart is even more of a visionary than Zuckerberg, and that there’s going to be a lot of pressure to sell.

Stewart readily admits he sold Flickr too early.

“If we had waited six months we would have made much more money. If we had waited a year we would have made 10 times more money,” he says. He regrets it now. But at the time, after the dotcom crash, the Nasdaq plummet, and September 11, deals just weren’t happening. All his advisers and investors told him to go for it. It was hard to know what to do.

In the wake of WhatsApp (a $19 billion sale to Facebook) and Beats ($3 billion to Apple) and even Instagram (a lousy $1 billion, Facebook again), $22 million now seems like the kind of money you dig out of your wallet to give a stranger at the bus stop. But for the team at Flickr, it was life-changing. Slack, on the other hand, is looking at something more like first class airfare.

Such temptations aren’t easy to resist. “We could sell it right now for a billion dollars,” Stewart says, and then shakes his head like he’s trying to wake up from a weird dream. “Which sounds fucking mental. But the thing is, those options aren’t going to go away.”

He admits that if the right offer comes along, the kind of offer that only three or four companies in the world could come up with, he would have to jump. But what is that? Five billion? Seven? Ten? It’s hard to know, because in Silicon Valley today, money has lost all meaning and value. It is an abstract construct that can be exchanged for homes and Teslas and handmade selvedge denim jeans flown in from Japan, but nobody really has any idea what constitutes “a lot” anymore. At some point however, he would be obligated to all those who’ve stuck with him and to all those who have given him money. Yet his ambition is to keep growing and building Slack on his own terms.

“I want to keep going,” he says. “And I think everyone else does too.” He’s hungry. He wants to win.